The present invention relates to a device for sealing off openings through the wall of a well tubular, which well tubular is a production tubing, a casing or a liner. Such a device is also referred to as xe2x80x98sliding sleevexe2x80x99, or when used for cementing as xe2x80x98cementing collarxe2x80x99.
It is well known that a well for producing hydrocarbons from an underground reservoir comprises a borehole that is lined with a well tubular in the form of a casing or a liner. The annular space between the outer surface of the well tubular and the inner surface of the borehole is filled with cement, which cement is put in place following inserting the casing in the borehole. Putting the cement in place is done by pumping a volume of cement through the well tubular and allowing it to rise in the annular space from the bottom of the borehole to the required level. When the borehole is deep and consequently the casing very long, single stage cementing is not possible because of the high pressures generated at the casing shoe. Therefore, cementing is done in stages. The first stage is cemented from the bottom to a pre-determined level. The second stage employs the use of a cementing collar or sliding sleeve that is an element of the casing. This cementing collar allows selectively placement of cement by uncovering holes in the wall of the well tubular at the level of the cementing collar. In order be able to pump the cement through the holes, a plug is set just below the holes. Then cement is supplied into the annular space through these holes. Having finalized the second stage, the holes are closed by adjusting the position of the sliding sleeve of the cement collar.
It is an object of the present invention to provide a device for sealing off openings through the wall of a well tubular that can easily be set and that has a good sealing ability.
In accordance with the invention there is provided a device for sealing off an opening through the wall of a well tubular, which device comprises a tubular spacer having an outer diameter allowing the spacer to be arranged in the well tubular, a first seal collar assembly and a second seal collar assembly arranged opposite ends of the tubular spacer, each seal collar assembly comprising an activator ring and an annular seal collar, the activator rings being interconnected by a cylindrical system of shape memory alloy which system contracts when the temperature of the cylindrical system reaches the transition temperature of the shape memory alloy, and wherein each annular seal collar is arranged so as to be compressed against the inner surface of the well tubular upon contraction of the cylindrical system of shape memory alloy.
In the specification and the claims, the term xe2x80x98shape-memory alloyxe2x80x99 is used to refer to an alloy that exhibits a shape-memory effect, wherein a complete recovery of a deformation undergone at a particular temperature takes place at heating. The skilled person is able to select a composition of the alloy material that exhibits the required effects at the temperatures prevailing in the well.
An advantage of the device according to the present invention is that is does not form a part of the well tubular. Therefore it can be set there where from an operational point of view a hole in the well tubular is needed that has to be closed after use.
The device according to the present invention can also be applied to seal off holes in the wall of a perforated casing. In this case the casing wall is perforated to allow production from an underground reservoir. In this case production management can be applied.
The device can also be used for repair jobs, wherein holes in a well tubular caused by corrosion and wear have to be closed.
Suitably each annular seal collar is arranged between the activator ring of the respective seal collar assembly and the tubular spacer.
In a preferred embodiment said cylindrical system is substantially coaxially arranged within the spacer. In this manner there remains a central passage for tools or fluid in the well tubular.
The cylindrical system can, for example, includes a tubular element of shape memory alloy.
Alternatively the system can include a plurality of rods of shape memory alloy, the rods being circumferentially spaced along the cylindrical system.